Abstract

Predicted order in low-dimensional electron systems, such as antiferromagnetic and crystalline quantum wires, non-Abelian fractional Quantum Hall States, and Bose-Einstein condensation of excitons in electron-hole bilayers, as well as expected improved performance of devices sensitive to thermal noise, motivates the development of techniques for cooling electrons in nanostructures into low millikelvin and micro-kelvin regime.

In a conventional dilution refrigerator with a base temperature of 5-20 mK the electrons in a nanostructure typically reach tens of mK. With the goal of reducing this figure below 1 mK we cool a sample in a helium-3 immersion cell mounted on a nuclear demagnetisation cryostat with a 0.3mK base temperature. In the prototype experiment a simple 2DEG sample is cooled via large Ohmic contacts and its temperature is measured with a noise thermometer attached via another contact. We investigate thermal transport in 2DEG and Ohmic contacts and derive a thermal model relating the temperatures of the sample and thermometer. This gives the electron temperature estimate of 1.5 mK achieved after reducing the heat leak to the sample to few femtowatt.

I will review the principles of dilution and demagnetisation refrigerators, and noise thermometry, compare our approach to cooling nanostructures to those taken by other groups, and discuss the proposed experiments in quantum point contacts.

Figure 1: Inside the He3 immersion cell